Various forms of flat tube and fin heat exchangers are known in which the fin (also known as an air center) have various louver or plain fin panel configurations for enhancing the heat transfer efficiency of the heat exchanger by creating turbulence in the air flow therethrough.
U.S. Pat. No. 4,535,839 discloses such a heat exchanger in which the panels of convoluted air centers are pierced in a roll forming process utilizing a first set of forming rollers with teeth configured to receive a strip of roll stock of a desired width and to roll the strip to simultaneously form convolutions and louvers prior to cutting the air center to a desired length. The air center then is reformed to pinch or crush the louvers in the end panels of the air center to close the end panels such that air will not escape through the sides of the heat exchanger. Such reforming, in one case, is performed by directing a cut to length air center through a second set of forming rollers that are configured to engage only the end panels of the air center to pinch louvers therein into a flat or closed position. It has been found that the reflattening step is not totally reliable. Consequently air bypassing at the end panels of the air centers is not completely eliminated. Another proposal has been to direct the louvered convolutions through a set of dies at a cutoff mechanism in order to crush the louvers on either side of either a crest or valley of the convolutions. Such dies are unable to fully crush all of the preformed louvers, and consequently, air bypass is not fully eliminated.
Yet another proposal leaves the end panels of a convoluted air center undeformed with only intermediate panels of the convolutions having louvers formed therein. This proposal is not fully practical since convolutions with louvers are formed in a continuous high speed processing operation and it is difficult to reset the rollers at the ends of the panel to prevent louvering. Furthermore, there is no way to assure registering a cut-off die with at unlouvered panels.
The present invention allows the use of a single set of convolution and louver piercing dies to form dammed panels in the air center for directing air flow through the air centers of a tube and fin heat exchanger so as to improve the heat transfer efficiency of the heat exchanger.
In one aspect, the present invention departs from the structure in the aforedescribed '839 patent by controlling air flow through the air center by selectively damming predetermined panels of a convoluted air center without requiring closure of only the end panels thereof.
In another aspect of the invention a flat tube and fin type heatexchanger has a fin formed with convolutions therein having a predetermined set of adjacent panels formed with louvers therein and with each of a set of adjacent louvered panels being connected to a second set of panels formed without louvers for forming air dams in the convolutions for channeling air flow axially through the air centers.
The present invention also includes a method in which convolutions and louvers are simultaneously formed in selected series of air center panels while generating a periodic dammed panel in the convolutions to axially channel air flow through the air centers of a flat tube and convoluted air center heat exchanger. The method comprises shaping a first plurality of convolutions in a strip of roll stock while simultaneously forming louvers in each of the panels in the convolutions; and periodically shaping a second plurality of convolutions in a strip roll without forming louvers therein.
The present invention in one embodiment includes the method of shaping the dammed panels only at a predetermined spaced ones of the panels in a continuously convoluted strip of roll stock and thereafter cutting the convolutions to a predetermined length so as to include at least two or more dammed panels in the convoluted strip of roll stock.
The present invention, in another embodiment, includes the method of shaping the dammed panels only at a predetermined spaced ones of the panels in a continuously convoluted strip of roll stock while corrugating the dammed panels along their length to reinforce them against crimping and thereafter cutting the convolutions to a predetermined length so as to include at least two or more corrugated, dammed panels in the convoluted strip of roll stock.
A further feature of the present invention is apparatus to form a convoluted fin with louvered panels and uncut dams. The apparatus includes a rotary forming disc set for forming an evaporator fin with a fixed multiple of convolutions and a fixed number of louvered panels on each revolution of the disc set. A preselected number of the teeth on the forming disc are ground flat (in one embodiment every eighth tooth is ground flat on a thirty two tooth forming disc) to prevent the disc set from louvering every nth panel in the convolutions to form a series of spaced air dams for channeling air flow through the evaporator unit.
Still another advantage of the present invention is the provision of apparatus including rotatable discs with cutting teeth and shaping teeth configured to corrugate the dammed panels along their length to reinforce them against crimping.
These and other objects, advantages and features of the present invention will become more apparent from the following description and drawings in which: